This invention relates generally to fueling control systems for internal combustion engines, and more particularly to an idle speed control system for an internal combustion engine.
In certain applications utilizing an internal combustion engine, the engine may be subjected to a rapid load increase. If fueling remains constant in such a situation, the engine torque output will decrease, and the rotational speed of the engine will decrease. If the rotational speed of the engine falls below a threshold level, the engine could stall. In order to prevent an engine from stalling, most engine fueling control systems maintain a minimum engine speed, known as the idle speed.
In the past, the idle speed of an engine was controlled by an xe2x80x9cidle screwxe2x80x9d that physically prevented the throttle plate of the carburetor from closing, thereby ensuring that a minimum amount of fuel would be supplied to the engine. However, because this was an open loop system, increasing the load on the engine, even very gradually, would eventually cause the engine to stall. In modern electronic engine control systems, an engine speed sensor works in conjunction with a feedback controller to maintain a minimum engine speed, or idle speed. With this feedback control system, gradually increasing the load on the engine will not generally cause the engine to stall if engine speed is maintained above the idle speed. However, a rapid increase in the engine load may cause the engine speed to temporarily drop below the idle speed, thereby resulting in an engine stall.
One application where an internal combustion engine may be subjected to rapid increases in loading is in engine-driven pumping operations. For example, if the viscosity of the liquid being pumped increases suddenly, or the pump inlet becomes obscured, engine load may rapidly increase. Another example of an application where an engine may be subjected to rapid increases in loading is engine-driven electric generating sets. For example, where the generator is idling and a device requiring a large amount of current, such as an electric motor, is coupled to the generator, engine load may likewise increase rapidly.
One of the most common applications where engines are frequently subjected to extreme, rapid loading increases is a marine craft propulsion system. Marine craft, unlike land vehicles, generally do not have braking systems. Therefore, the operator of a marine craft decreases velocity by shifting into a drive mode opposite to the direction of travel. This same procedure is used irrespective of whether the marine craft is in forward drive mode or reverse drive mode.
Generally, marine propulsion systems are controlled by a system known as a xe2x80x9csingle lever controlxe2x80x9d. Such single lever controls comprise a lever that is connected to both the speed control and the transmission of the marine propulsion system. The operation is such that in a neutral position, the transmission is held in neutral and the engine is maintained at its idle speed. When the control lever is shifted in one direction or the other from neutral, the transmission is engaged, typically via a clutch, in the forward drive mode or the reverse drive mode, while the engine is maintained at idle. If the operator continues to move the single lever control in the same direction, then the throttle is progressively opened, but only after the shifting has been completed.
This single lever control is very effective and easy to use for the operator. However, this type of system has disadvantages when the transmission is utilized to brake the travel of the marine craft. For example, if the marine craft has been traveling in one direction at some substantial speed, and the transmission is shifted into neutral, the marine craft will continue to move in that direction and the propeller will be rotated by the drag of the water. Furthermore, the engine speed will be returned to the idle speed.
Therefore, when the operator brakes the marine craft by immediately engaging the transmission to drive in a direction opposite the direction of travel, there will be a relatively high load placed on the engine, because it must overcome the drag on the propeller in order to reverse its direction of rotation. When the engine is operating at the idle speed, this drag on the propeller may be sufficient to cause a drop in engine speed sufficiently below the idle speed to result in an engine stall. Therefore, there is a need for a feature of a marine propulsion system to prevent stalling when the engine and transmission are used to brake vehicle travel.
Because marine propulsion systems are prone to stalling during these maneuvers, some methods exist in the prior art to prevent stalling when the engine and transmission are used to brake vehicle travel. One such method is disclosed in Hoshiba U.S. Pat. No. 6,102,755, granted Aug. 15, 2000, herein incorporated by reference. Hoshiba discloses a method for preventing stalling during the foregoing conditions wherein engine speed is increased above idle speed when a reversing of the direction of travel is detected. Hoshiba discloses a sensor for determining when the position of a single lever control changes from a position indicating travel in one direction to a position indicating travel in the opposite direction.
Another method to prevent stalling in a marine craft engine when a gear selection mechanism is moved from a neutral position to a forward or reverse position is disclosed in Ruman U.S. Pat. No. 5,836,851, granted Aug Nov. 17, 1998, herein incorporated by reference. Ruman discloses another method for preventing stalling during such conditions wherein the gain coefficients (factors) of a proportional, integral, and differential (PID) engine controller are changed to effectively increase the idle speed of the engine during gear selection mechanism articulation. Ruman discloses a sensor for determining a movement of the gear selection mechanism from a neutral position to a forward or reverse position, and the gain coefficients are modified when the sensor indicates such a movement.
While these and other prior art systems generally perform adequately for the applications for which they are designed, each requires the addition of a dedicated sensor for detecting the actuation of a control device, and a signal path between the sensor and an electronic engine controller that includes an interface for, and that is responsive to, signals from the sensor. Therefore, a need exists for a method to prevent stalling when an engine and transmission are used to brake vehicle travel that does not require additional sensors, such as for sensing the actuation of a control device.
Some applications where an engine is subjected to rapid increases in loading, such as those mentioned above, are not in response to the actuation of a control device, but rather are due to a change in operating conditions. In these applications, stalling cannot be prevented by the methods disclosed in Hoshiba, Ruman, or by other prior art systems, because there is no control device responsible for the load increase to which a sensor may be attached. Therefore, in these applications, a need also exists for a method to prevent stalling.
According to one aspect of the invention, a system is provided for controlling idle speed of an internal combustion engine. The system comprises an engine speed sensor producing an engine speed signal indicative of a rotational engine speed of an internal combustion engine. The control circuit controls the rotational speed of the engine between an idle speed reference and a maximum speed reference. The control circuit also modifies the idle speed reference as a function of the engine speed.
Illustratively according to this aspect of the invention, the control circuit increases the idle speed reference from a first idle speed value to a second higher idle speed value as a function of the engine speed signal.
Further illustratively according to this aspect of the invention, the control circuit increases the idle speed reference to the second idle speed value if said engine speed signal indicates a rotational engine speed greater than a threshold engine speed value for at least a first predefined time period.
Further illustratively according to this aspect of the invention, the control circuit increases the idle speed reference to the second idle speed value if the engine speed signal indicates a rotational engine speed less than the threshold engine speed subsequent to indicating for at least the first predefined time period a rotational engine speed greater than the threshold engine speed.
Further illustratively according to this aspect of the invention, the control circuit decreases the idle speed reference from the second idle speed value to the first idle speed upon the expiration of a second predefined time period.
Further illustratively according to this aspect of the invention, the control circuit decreases the idle speed reference from the second idle speed value to the first idle speed at a predetermined rate.
Alternatively illustratively according to this aspect of the invention, the control circuit includes an engine speed control strategy. The engine speed control strategy comprises a means for generating a reference engine speed as a function of a torque request, a means for generating the idle speed reference, a means for generating the maximum speed reference, and a speed governor configured to control the rotational engine speed of the engine between the idle speed reference and the maximum speed reference. The means for generating the idle speed reference is responsive to the engine speed signal to modify the idle speed reference.
According to another aspect of the invention, a method is provided for controlling minimum rotational speed of an internal combustion engine. The method comprises the steps of determining a rotational engine speed of an internal combustion engine, determining an engine acceleration rate as a function of the rotational engine speed of the engine, and controlling a minimum rotational speed of the engine as a function of the rotational engine speed of the engine and the engine acceleration rate.
Illustratively according to this aspect of the invention, controlling the minimum rotational speed of the engine includes increasing the minimum rotational speed from a first speed value to a second higher speed value if the rotational engine speed is greater than a threshold speed value and the engine acceleration rate is less than a predefined engine acceleration rate.
Further illustratively according to this aspect of the invention, controlling the minimum rotational speed of the engine includes increasing the minimum rotational speed from the first speed value to the second higher speed value if the rotational engine speed is greater than the threshold speed value for at least a first predefined time period.
Further illustratively according to this aspect of the invention, controlling the minimum rotational speed of the engine includes decreasing the minimum rotational speed from the second speed value to the first speed value upon the expiration of a second predefined time period.
Further illustratively according to this aspect of the invention, controlling the minimum rotational speed of the engine includes decreasing the minimum rotational speed from the second speed value to the first speed value at a predetermined rate.
According to another aspect of the invention, a system is provided for controlling idle speed of an internal combustion engine. The system comprises an engine speed sensor producing an engine speed signal indicative of rotational speed of an internal combustion engine, and a control circuit controlling the rotational speed of the engine between an idle speed reference and a maximum speed reference. The control circuit temporarily increases the idle speed reference from a first idle speed value to a second higher idle speed value if the engine speed signal drops from a threshold rotational speed value.
Illustratively according to this aspect of the invention, the control circuit is increases the idle speed reference from the first idle speed value to the second idle speed value for a predefined time period.
Further illustratively according to this aspect of the invention, the control circuit returns the idle speed reference to the first idle speed value upon expiration of the predefined time period.
According to another aspect of the invention, a method is provided for controlling idle speed of an internal combustion engine. The method comprises the steps of determining a rotational speed of an internal combustion engine, controlling the rotational speed of the engine between an idle speed reference and a maximum speed reference, and temporarily increasing the idle speed reference from a first idle speed value to a second greater idle speed value if the rotational speed drops from a threshold rotational speed value.
Illustratively according to this aspect of the invention, temporarily increasing the idle speed reference includes increasing the idle speed reference from the first idle speed value to the second idle speed value if the rotational speed is greater than the threshold rotational speed value for at least a first predefined time period.
Further illustratively according to this aspect of the invention, temporarily increasing the idle speed reference includes decreasing the idle speed reference from the second idle speed value to the first idle speed value upon the expiration of a second predefined time period.
Further illustratively according to this aspect of the invention, temporarily increasing the idle speed reference includes decreasing the idle speed reference from the second idle speed value to the first idle speed value at a predetermined rate.
Further illustratively according to this aspect of the invention, the first predefined time period is approximately ten seconds and the second predefined time period is approximately four seconds.